The youth massed on downtown streets, from 1st Mariner Arena on the west side to "The Block" on East Baltimore Street, and south through Baltimore's Inner Harbor, Moses said. He couldn't confirm the exact number of youths, though witnesses likened it to one of the stadiums emptying out.

Moses said, "It was definitely a lot — a lot of kids, a lot of police."

Baltimore police spokesman Anthony Guglielmi described the scene as an "abnormally high number of juveniles in the downtown area."

He said police were investigating to determine what drew the teens downtown.

"We've heard informally there was some sort of meet-up on social media," he said.

Several witnesses who were dining at the harbor's restaurants said that around 9:30 p.m. several streets were blocked off, including Calvert and Pratt streets, as they attempted to leave the Inner Harbor Saturday night. The witnesses said that police escorted them to their car.

Police in the downtown area called in officers from other districts to help with crowd control, according to the department.

"With the weather being warm now, we tried to take a proactive approach," Moses said. "We kept it moving, because once you let them stand still, problems can arise."

Guglielmi said police headquarters has received one report of an officer using a Taser that night but said he had no details of the incident and could not say whether it was related to the crowd.

"We had a very heavy presence of police officers in the downtown area," he said. "Curfew laws were enforced to make sure the kids were safe."

Just getting accepted to Johns Hopkins University was an accomplishment for Jeremy Huber. Getting recruited to play lacrosse for a program that has won nine national championships was another thing entirely.